This proposal complements our current NIH-CIA grant DK02244 which is designed to examine predictors of obesity. During the last two years we have completed the recruitment of 56 normal-weight prepubertal females. These children have been admitted twice to the GCRC for 4 days each, where ad libitum caloric intake has been recorded and where they have undergone duplicate baseline testing of the following measurements: energy expenditure, total (24-hour) energy expenditure, resting energy expenditure, free-living energy expenditure, sedentary energy expenditure and non-sedentary energy expenditure. As well, each of their parents have undergone weight history and activity questionnaires, anthropometric measurements, abdominal computer tomography and dual energy x-ray absorptiometry. In this protocol we will conduct a longitudinal study to repeat these measurements in the children yearly. By doing so we will be able to track energy expenditure and body composition through their pubescence, to relate them to parental characteristics, and to document temporal changes which will help establish cause vs. effect relationships.